This invention relates to the conversion of hydrocarbons to higher hydrocarbons. This invention more particularly relates to the conversion of normally gaseous alkanes into normally liquid hydrocarbons. This invention is especially concerned with the conversion of natural gas to higher hydrocarbons, preferably normally liquid hydrocarbons.
The composition of natural gas at the wellhead varies. For example, the methane content of natural gas may vary from about 40 to about 95 vol. %. Other constituents of natural gas include ethane, propane, butanes, pentanes (and heavier hydrocarbons), hydrogen sulfide, carbon dioxide, helium and nitrogen.
Natural gases are classified as dry or wet depending on the amount of condensable hydrocarbons contained in it. Condensable hydrocarbons generally comprise C.sub.3 + alkanes although some ethane may also be included. Gas conditioning is conventionally employed to alter the composition of wellhead gas, processing facilities usually being located in or near production fields. Conventional processing of wellhead natural gas yields processed natural gas containing at least a major amount of methane that also yield natural gas liquids containing, predominantly, C.sub.3 + alkanes.
Considerable attention has been devoted to finding economic means for producing synthetic fuels from natural gas or other feedstock composed of lower alkanes. One approach which has been extensively studied comprises natural gas to synthesis gas (mixtures comprising CO and H.sub.2) which is then either converted directly to higher hydrocarbons (broadly referred to as a "Fischer-Tropsch" conversion) or first converted to methanol which is subsequently converted to higher hydrocarbons (e.g., by use of the Mobil methanol-to-gasoline processes). A substantial difficulty with both of these synthesis gas-based methods is the formation of oxygenates, which complicates further processing of liquid products using conventional petroleum refining techniques. As demonstrated by the Sasol plants in South Africa such further processing requires customized refining techniques, particularly adapted to the unique feedstock produced. A process capable of converting methane and/or lower alkanes to hydrocarbons compatible with conventional refinery feedstock would therefore be of substantial value to the industry.
Large-scale use of natural gas often requires a sophiscated and extensive pipeline system. Liquefacation has also been employed as a transportation means, but processes for liquifying, transporting and revaporizing natural gas are complex and energy-intensive and require extensive safety precautions. Transport of natural gas has been a continuing problem in the exploitation of natural gas resources. It would be extremely valuable to be able to convert natural gas to more readily handable or transportable products. Moreover, improved methods for the conversion of natural gas would be of value to the chemical industry.
One object of this invention is a method for converting natural gas, especially wet natural gas, to higher hydrocarbons, especially normally liquid hydrocarbons. A related object is a method for converting lower alkanes to higher hydrocarbon products which are compatible with conventional petroleum refinery feedstocks for the purpose of further processing to more valuable hydrocarbon products. A further object of this invention is a method for converting natural gas to more easily transportable products. A still further object of this invention is an improved method for converting natural gas to higher hydrocarbon products wherein the yield of normally liquid hydrocarbohs is enhanced.
Other aspects, objects and the several advantages of the invention will become to those skilled in the art upon reading this disclosure and the appended claims.